1. Field of the Invention:
The invention relates generally to the fabrication of integrated circuit bipolar transistors, and more particularly, to a method for improving the radiation hardness of such transistors.
2. Description of the Related Art:
Radiation can degrade the performance of bipolar integrated circuit transistors. For example, exposure of such transistors to high energy x-ray or gamma ray radiation can lead to premature device failure. Radiation damage can occur, for example, as a result of the generation of electron-hole pairs in the passivation oxide and in the glassification which typically is disposed between the passivation oxide and packaging that houses the integrated circuit.
Ordinarily, negatively charged electrons and positively charged holes compensate each other in the oxide and in the glassification. High energy x-ray and gamma ray radiation, however, can produce electron-hole pairs. The electrons can more readily escape from the oxide or the glassification, leaving behind uncompensated positively charged holes. Unfortunately, the presence of such uncompensated positively charged holes can degrade transistor performance.
While earlier integrated circuit bipolar transistors generally have been acceptable, there have been shortcomings with their use. In particular, when such prior transistors are used in radiation intensive environments, such as in spacecraft, their performance often tends to deteriorate due to the presence of uncompensated holes in the oxide or glassification.
Thus, there has been a need for integrated circuit bipolar transistors that have improved resistance to radiation damage. The present invention meets this need.